PMC

Protein isoforms of Painless and Drosophila TRPA1. (a) Painless. (b) TRPA1. A.R. ankyrin repeats, NT N-terminal domain, TAC TRP ankyrin cap domain

Phylogenetic tree and cartoons of TRP channels from C. elegans (c; green), Drosophila melanogaster (d; red), and Homo sapiens (h; black). The TRPN channel from Danio rerio (dr; zebrafish; blue) is also included. To generate the tree, we used the predicted transmembrane segments of each TRP channel (http://www.cbs.dtu.dk/services/TMHMM/) in combination with the following online program: http://www.genome.jp/tools/clustalw/. Indicated on the TRP cartoons are ankyrin repeats (A.R.), coiled coil domains (cc), and the TRP domains, which include TRP boxes 1 and 2 (, ). TRPV proteins include only TRP box 1, rather than the full TRP domain. The N- and C-termini are the left and right ends of the TRP structures. The TRP termini are situated on the cytoplasmic side of the lipid bilayer

Model for activation of Drosophila TRP and TRPL. (a) The fly phototransduction cascade is not active, and the TRP and TRPL channels are closed in photoreceptor cells maintained in the dark. (b) The light-activated phototransduction cascade. (1) Light activation of rhodopsin. (2) GTP is exchanged for GDP on the Gα subunit (G_qα; also known as Gα49B) and the βγ subunit dissociates from the α subunit. (3) Activation of PLC (phospholipase Cβ) catalyzes the hydrolysis of PIP₂ (phosphoinositide-4,5-bisphosphate (PIP₂) into DAG (diacylglycerol), IP₃ (inositol-1,4,5-trisphosphate), and H⁺ (proton). (4) The major products of the DAG lipase (encoded by the inaE locus) are 2-MAG (2-monoacylglycerol) and a saturated FA (fatty acid). Not shown are the minor products: 1-MAG and a polyunsaturated FA (PUFA). (5) Activity of an unknown MAG lipase catalyzes the production of a PUFA and glycerol. (6) TRP and TRPL are activated, leading to influx of Ca²⁺ and Na⁺. The cleavage of PIP₂ (step 3) is proposed to contribute to activation of TRP and TRPL through a change in curvature of the plasma membrane, thereby creating mechanical force